You're on your own. Experience is the best teacher.
I've had some luck using splines to predict the stresses that will form under various curvatures formed by lines bending under their own weight and passing through fixed support points. If you have the shape of a beam described as deflection vs distance, then by taking successive derivatives you can arrive first at curvature, then moment * EI, shear force distribution and lastly support loads. Do for each configuration as the pipeline is lowered into the trench.
"Tubular Steel Structures-Theory and Design" by Troitsky", 2nd Edition, chapter 9 on aboveground pipelines, chapter 10 on underground pipelines and chapter 11 on underwater pipeline should be a good starting point. There is a ton of equations in these three chapters. There could be an updated edition as this book is sponsored by the James F. LncolnArc Welding Foundation with a copyright of 4/1982.
Who is an expert - Everyone!, but especially the lowering in foreman who does this day in day out and knows if he drops it or the pipe bends he's out of a job.
This area is one which always confuses my offshore colleagues who study to death the installation forces on the pipe, bending moments, tension etc etc
Onshore you just make sure the machine won't fall over in the ditch and then the actual lowering is undertaken "by eye". If it all goes horribly wrong and the pipe gets bent, then you just lift it out, cut it out and put a new one back in - then get a new lowering in foreman or sideboom / crane / digger operator - whoever got it wrong.
I've never seen any reference or regulation specifically referring to lowering in, but if anyone appears I'll put it away for future reference.
Key aspects you can look at include a basic beam bending with multiple point loads to simulate the pipe being picked up by more than one machine - Usually minimum of three machines - with a check for bending stress, and local buckling check. Standard equations apply.
The next big check is weight capacity of the various machines at the lift distance required. ~This is what usually governs the number and type of machines. It's where the accidents happen when you exceed the capacity of the boom or crane. Big pipes with a wide trench are especially vulnerable. At full extension, the load capacity is about 25% of the "rated" or nameplate capacity. Hence it might start as a 30tonne machine, but at an extension of 7m, with counterweight out, reduces to approx. 7 tonnes.
This is a famous video showing what happens when you get it wrong - I think they blamed it on the wind, but I think they just got it wrong with weight or something collapsed at the far end..
Not only the foremen as mentioned by L.I. but also the crane operators. Unfortunately the crane operators will be most of the time blamed which in several instances they have little to do with the engineering calculations, conditions of soils, maintenance of equipment and winds when they are told to setup for lifts.
